1. Field of the Invention
This invention relates to a radiation image recording and read-out apparatus for exposing a stimulable phosphor to a radiation to have a radiation image stored therein, scanning the stimulable phosphor with stimulating rays to cause the stimulable phosphor carrying the radiation image stored therein to emit light in proportion to the radiation energy stored, detecting the emitted light and converting it into an electric signal, and reproducing a visible image by use of the obtained electric signal. This invention particularly relates to a radiation image recording and read-out apparatus in which the stimulable phosphor is circulated and reused for recording radiation images.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted from the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318, and 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet comprising the stimulable phosphor is first exposed to a radiation passing through an object to have a radiation image stored therein, and is then scanned with stimulating rays which cause it to emit light in proportion to the radiation energy stored. The light emitted from the stimulable phosphor sheet when the sheet is exposed to the stimulating rays is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce a visible image having an improved quality, particularly a high diagnostic efficiency and accuracy. The finally obtained visible image may be reproduced in the form of a hard copy or may be displayed on a cathode ray tube (CRT). In this radiation image recording and reproducing system, the stimulable phosphor sheet is used to temporarily store the radiation image in order to reproduce the final visible image therefrom in a final recording medium. For economical reasons, therefore, it is desirable that the stimulable phosphor sheet be used repeatedly.
Further, in a mobile X-ray diagnostic station such as a traveling X-ray diagnostic station in the form of a vehicle like a bus which is provided with a radiation image recording and read-out apparatus for use in the aforesaid radiation image recording and reproducing system and moves from place to place to record radiation images for mass medical examinations, it is disadvantageous to load a mobile X-ray diagnostic station with a number of stimulable phosphor sheets, and the amount of the stimulable phosphor sheets which can be loaded on the mobile X-ray diagnostic station is limited. Therefore, it is desired to load the mobile X-ray diagnostic station with stimulable phosphor sheets which can be used repeatedly, once store the radiation images of the objects in the stimulable phosphor sheets, transfer the electric image signals read out from the stimulable phosphor sheets into a recording medium having a large storage capacity, such as a magnetic tape, and circulate and reuse the stimulable phosphor sheets for further image recording and read-out operations, thereby to obtain the radiation image signals of many objects. Further, when image recording is conducted continuously by circulating and reusing the stimulable phosphor sheets, it becomes possible to increase the image recording speed in mass medical examination. This is very advantageous in practical use.
In order to reuse stimulable phosphor sheets as described above, the radiation energy remaining in the stimulable phosphor sheet after it is scanned with stimulating rays to read out the radiation image stored therein should be eliminated or erased by the method as described, for example, in Japanese Unexamined Patent Publication No. 56(1981)-12599 or U.S. Pat. No. 4,400,619. The stimulable phosphor sheet should then be used again for radiation image recording.
Accordingly, it is desired that there be combined into a single apparatus: an image recording section for exposing each circulatable and reusable sheet composed of a stimulable phosphor to a radiation passing through an object, an image read-out section for reading out the radiation image stored in the stimulable phosphor sheet, and an erasing section for erasing the radiation energy remaining in the stimulable phosphor sheet after the readout step for the purpose of again recording another radiation image therein. This is because such an arrangement would make it possible to easily load the apparatus on the mobile X-ray diagnostic station to conduct medical examinations at different locations. Such an apparatus could also be easily installed in a hospital or the like. This is very advantageous in practical use.
However, in the radiation image recording and read-out apparatus as described above, when the image readout section and the erasing section are housed in the same frame, the following problem arises. In the image read-out section, the stimulable phosphor sheet carrying a radiation image stored therein is exposed to and scanned with stimulating rays to sequentially release the radiation energy stored in the sheet as light emission, and the emitted light is detected and converted into an electric image signal. The photoelectric read-out means such as a photomultiplier which is used in the read-out step must have a very high sensitivity since the amount of light emitted from the stimulable phosphor sheet upon stimulation thereof is very small. Thus the photoelectric read-out means is susceptible to disturbance. On the other hand, in the erasing section, the stimulable phosphor sheet must be exposed to erasing light having a very high intensity in order to release the radiation energy remaining in the sheet after the read-out step. For this purpose, for example, many fluorescent lamps are positioned in the erasing section. Accordingly, erasing light emitted in the erasing section constitutes a very serious source of disturbance in the read-out operation in the image read-out section. Therefore, the image read-out section must be completely shielded from erasing light. That is, a light shielding means must be provided to prevent erasing light from entering the image read-out section.